Spark plug



De.31, 1935. J. TETLOW SPARK PLUG Filed D90. 29, 1932 OW /l t I INVENTOR 7" f ATTORNEY Patented Dec. 31, 1935 UNITED sTATEs PATENT oFPlcE SPARK PLUG Lewis J. Tetlow, Holyoke, Application December 29, 1932, serial No. 649,411

s claims. (o1. 12a-169) An additional feature in connection'with the skirted tip isthe use of a helix of copper or other metal capable of carrying heat rapidly wrapped around the central electrode for a portion of its length toward the terminals.

In the drawingz- Figure 1 is a central section thru a truck plug embodying my invention.

Figure 2 isa modified form. Y

' In the modication shown in Figure 1 the porcelain cylinder or core Id is of previously known type of body having a conical surface Il to receive an upper gasket I2 which I preferably make of brass and a similar opposite conical surl face I4 which seats iirmly on the lower gasket l5 which is of asbestos covered with copper. The

central porcelain body I0 has at its lower portion a nose I6 having a flat bottom face preferably slightly cupped as at Il.

Thru the center of the core are two bores, the smaller numbered I8 receiving loosely the central electrode and the larger bore 2l furnishing a well which may extend down as far as the center -of the integral enlarged portion of the core and providing ample space to receive a pipe of copper tightly engaging the central electrode 25 but spaced from the cylindrical wall of the bore 2|. The pipe 25 may extend to the bottom 26 of the largerbore or it may terminate short of this point but preferably tightly engages the electrode and is permanently secured to the base cap 23 in which the central electrode is firmly embedded and to which the terminal plug 23 threaded as at 30.

The ring point of the electrode is made fairly .large and its outer curve 33 is preferably ogival and extends considerably above the flat. end I1 of the nose of the electrode body having a skirt 34 which should be suiliciently large to give an appreciableA clearance between its inside surface 35 and the conical wall of the nose portion I6 of the body. l A

While the sparking point may be secured to the central electrode 25 in any desired manner I nd it most eilicient to thread the electrode as at 31 and to use a cement on these threads which can be softened in boiling water. Such a cement is readily obtainable and gives a most rm joint as long as the tip is kept dry. Since it is my intention to replace the tip when pitted it is best to use a cement which under extraordinary conditions will be' readily releasable. There is no tendency toward moisture in the plug and there- 'fore the placing of the tip in boiling water would .be an extraordinary condition. The shape of tip 10 or point shown in Figure 1 is very satisfactory but I also have had excellent results with the somewhat modified form shown in Figure 2. This modiied tip has a skirt portion 40, a solid intermediate conical portion 4I and a very heavy 15 tip portion I2, the latter being threaded for a. portion of its length as at 43 to receive the centrai electrode 20.

While I prefer to add a' very slight iillet as at I5 to the junction between the nearly cylindrical tip I2 and the conical portion Il and to round oi slightly as at 46 the junction between the skirt and the conical portion, I have nevertheless found in practice that the sharp angles at these points are not detrimental. The smoother curve however is substantially as easy to make and gives a somewhat better appearance.

The modification shown in Figure 2 includes an outer insulating body 50 secured as by cement in a bushing 5| and having a large central bore 52 for receiving a core 53 which core carries the conical end 5I tting snugly up against the mica washer or washers 55 engaging the metal washer 56 which is preferably spun into a groove 51 in the bottom rim of the bushing 5I. Between the core 53 and the body 50 is a sleeve 58 of some tough materialsuch as mica which not only serves to hold the core and body together but also prevents a crack extending from the electrode 20 to the outer surface of the insulator or to the bushing 5l. A second bore 60 in the top of the body 50 provides ample'space to receive a helix GI of copper wire tightly wound on the central eleotrode 20 but spaced'from the cylindrical wall of the bore. The helix El may rest on the core 53 as shown or it may terminate Ashort of the core but is preferably tightly wrapped on the electrode and is permanently secured to the base cap 28 in which the central electrode is rmly embedded the same as in Figure 1. VIt will be seen that the electrode is free of the insulator being supported entirely by the tip 4l and cap 28.

The method which I follow in assembling the plug illustrated in Figure 2 is as follows: The washer 56 is spun in place on the bushing or nut 5|. the sleeve 58 is cemented in the body 50 and the latter is then cemented to the nut 5I, one or more mica washers 55'are placed on the core 53 and after applying a bit of cement to the core it is inserted into the sleeve until the shoulder thereof carries the insulating washer against the ledge 56. A small amount of cement is now applied to the top 64 and bottom 65 of the insulator body, the electrode is then threaded through the body and after putting cement on the threads 43 the cap or tip 42 is screwed into place and the cap 2B is spun on the body. The placing of the helix on the electrode is a separate operation preferably being done at the same time as the electrode is pressed into the cap 28 before the assembling process is started. The nal step is the baking of the plug after which it is supplied with a con-- nector 29 and screwed into a bushing of the def sired size.

What I claim is:

1. In a spark plug, an insulating member having a nose, an electrode passing thru said member-and projecting beyond the nose, and a ring tip on the end of the electrode, said tip having a skirt covering the sides of the end of the nose but slightly spaced therefrom.

` 2. The device of claim 1 in which the nose has a ilat iace the tip covers the flat face and the skirt is conical.

3. The device xof claim 1 in which a helix of copper is tightly wound on the tipless end of the electrode.

4. A sparking point for the central electrode of a spark plug consisting of a tip having a bore to receive the central electrode and having an upstanding skirt adapted to protect the'nose portion of an insulating body said skirt having an inside diameter greater than the outer diameter of the nose portion. 5

5. The device of claim 4 in which the skirt and the/tip are each cylindrical and the intermediate portion tapers from the smaller tip portion to the larger skirt portion.

6. A spark plug having a central core having 10 a bore therethrough of two diameters,.a central electrode in the smaller bore, and a helix tightly wound upon the central electrode and positioned in the larger bore. A

7. A spark plug comprising an insulator con- 15 sisting of a central core having a cylindrical por.'a tion and a conical portion, an insulating sleeve entirely surrounding the cylindrical portion of the core, a bushing permanently secured to the sleeve, an electrode thru thecore, a cap on the go sleeve and a second cap on the conical portion, l v

said electrode being securedto the sleeve cap and having threaded engagement with the second can. whereby the two core portions are held together and said second cap constitutes one electrode of g5 the spark gap. 1

8. 'A sparking point for'the central electrode of a spark plug consisting of a tip having a bore to receive the central electrode and having an upstanding skirt adapted to protect the nose w portion of an insulating body, the outer contour y of the tip and skirt being an ogive curve.

Lewis J. mow. 

